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In January, Circuit Cellar introduced a new section, Tech the Future, which dedicates page 80 of our magazine to the insights of innovators in groundbreaking technologies.

We’ve reached out to a number of graduate students, professors, researchers, engineers, designers, and entrepreneurs, asking them to write short essays on their fields of expertise, with an emphasis on future trends.

Their topics have included high-speed data acquisition, Linux home automation, research into new materials to replace traditional silicon-based CMOS for circuitry design, control system theory for electronic device DIYers, and how open-source hardware will make world economies more democratic and efficient.

Our contributors have been diverse in more than just their topics. They have been talented

Tech the Future essayist Fergus Dixon designed this DNA sequencer, the subject of an article in the May 2013 issue of Circuit Cellar.

The one thing they have in common? They keep a close eye on the ever-changing landscape of technological change. And their essays have helped our readers focus on what to watch. We compensate authors for the essays we choose to publish, and we are eager to hear your suggestions on subjects for Tech the Future.

If you are an innovator interested in writing an essay for Tech the Future, e-mail me (editor@circuitcellar.com) with the topic you’d like to address and some information about yourself. If you are a reader who wants to hear from someone in particular through Tech the Future or has a suggestion for an essay topic, please contact me.

• Saptarshi Das, a nano materials researcher who holds a PhD in Electrical Engineering from Purdue University, focusing on the urgent need for alternatives to silicon-based CMOS. These alternative materials, now the subject of extensive scientific research, will be game changers for the microelectronics and nanoelectronics industries, he says.

• Fergus Dixon, an Australian entrepreneur and designer of the popular software program “Simulator for Arduino,” explaining why open-source hardware is a valuable tool in the development of new medical devices. Design opportunities for such devices are countless. Hot technologies developed for 3-D printing and unmanned aerial vehicles (UAVs) have direct medical applications, including 3-D-printed prosthetic ears and nanorobots that utilize UAV technology.

Enjoy these articles and others online. In the meantime, I’ll be checking my e-mail for what you would like to see featured in Tech the Future.

The RP6v2 is a C-programmable autonomous mobile robot system designed for hobbyists and educators at universities, trade schools, and high schools. The system includes a CD with software, an extensive manual, plenty of example programs, and a large C function library. All library and example programs are open-source GNU general public license (GPL).

The autonomous mobile robot system has a large payload capacity and expansion boards, which may be stacked as needed. It receives infrared (IR) codes in RC5 format and includes integrated light, collision, speed, and IR-obstacle sensors. Its powerful tank drive train can drive up steep ramps and over obstacles.

The RP6v2’s features include an Atmel ATmega32 8-bit RISC microcontroller, AVR-GCC and RobotLoader open-source software for use with Windows and Linux, six PCB expansion areas, two 7.2-VDC motors, an I2C bus expansion system, and a USB interface for easy programming and communication.
The fully assembled RP6v2 robotic system costs $199.

The SP-7W61 and the SP-1061 smart panels are based on the Texas Instruments 1-GHz Sitara AM3715 Cortex-A8 processor and an Imagination Technologies integrated PowerVR SGX graphics accelerator. The products support multiple OSes—including Linux 2.6.37, Android 2.3.4, and Windows Compact 7—making them well suited for communications, medical and industrial control, human-machine interface (HMI), and transportation applications.

The SP-7W61 (7” and 16:9) and the SP-1061 (10” and 4:3) have a low-power, slim, fanless mechanical design and a high-value cost/performance (C/P) panel PC module that uses powerful and efficient components. Compared with other x86 HMI or open-frame products, the SP-7W61 and the SP-1061 successfully keep power consumption to less than 5.9 W, which is half the typical rate. The smart panels feature multiple display sizes and low power consumption options. They can be implemented into slim and thin chassis types (e.g., for HMI, control panels, or wall-mount controllers).

ADLINK provides full support on software customization based on different platforms. A virtual machine or software development kit (SDK) is provided with related documentation for different platforms, so users can easily set up the software environment.
Contact ADLINK for pricing.

The APSYN420B is a 0.65-to-20-GHz frequency synthesizer with a 0.001-Hz resolution and 0.1° phase resolution. The synthesizer provides a nominal output power of 13 dBm into 50 ?. The module features a high-stability internal reference that can be phase-locked to a user-configurable external reference or used in a master-slave configuration for high phase coherence.

The APSYN420B’s key features include low phase noise, fast switching (settling time is typically 20 µs with a 20-µs frequency update), and an internal OCXO reference that can be configured for high phase coherence between multiple sources. The synthesizer offers USB and LAN interfaces and consumes less than 10 W when powered from an external 6-VDC supply.

The APSYN420B’s modulation capabilities include angle, pulse, pulse trains, and pulsed chirps. Linear, logarithmic, or random-frequency sweeps can be performed with combined modulation running. Frequency chirps (linear ramp, up/down) can also be accomplished. The device can accept external reference signals from 1 to 250 MHz.

Applications for the APSYN420B include automatic test equipment, satellite, and other telecommunications needs. The APSYN420B is designed for a 0°C-to-45°C operating temperature range and weighs less than 2 lb in a compact 2.4” × 4.2” × 8.3” enclosure.
Contact Saelig for pricing.

The SoC’s media hardware accelerators enable features such as 4× HD 1080p video encoding/decoding including Blu-ray support at 60 frames per second, image/voice recognition, and high-resolution 3-D graphics with almost no CPU load. These implemented hardware modules also execute the display content improvements needed for HMI/navigation data similar to movie/DVD handling.
Contact Renesas for pricing.

The KNX Gateway enables HAI by Leviton’s Omni and Lumina Ethernet-based controllers to communicate with and control KNX devices through KNX’s standardized network communications bus protocol. You can use an HAI by Leviton interface or automated controller programming to control KNX devices (e.g., lighting devices, temperature and energy management, motors for window coverings, shades, and shutters) in homes and businesses.

The KNX Gateway maps specific data points of each KNX device to a unit or thermostat number on the HAI by Leviton controller. The interface between the KNX Gateway and the HAI by Leviton controller utilizes a RS-485 serial connection.

Compatible controllers include HAI’s OmniPro II home-control system, Omni IIe, Omni LTe, Lumina Pro, and Lumina. The KNX Gateway is powered by either a power over Ethernet (PoE) connection or a 12-to-24-V AC/DC converter.
Contact Leviton for pricing.

The LTC3863 is a high-voltage inverting DC/DC controller that uses a single inductor to produce a negative voltage from a positive-input voltage. All of the controller’s interface signals are positive ground referenced. None of the LTC3863’s pins are connected to a negative voltage, enabling the output voltage to be limited by only the external components selection.

Operating over a 3.5-to-60-V input supply range, the LTC3863 protects against high-voltage transients, operates continuously during automotive cold crank, and covers a broad range of input sources and battery chemistries. The controller helps increase the runtime in battery-powered applications.

It has a low 70-µA quiescent current in Standby mode with the output enabled in Burst Mode operation. The LTC3863’s output voltage can be set from –0.4 to 150 V or lower at up to 3 A typical, making it well suited for 12-or-24-V automotive, heavy equipment, industrial control, telecommunications, and robotic applications.

The LTC3863 drives an external P-channel MOSFET, operates with a selectable fixed frequency between 50 and 850 kHz, and is synchronizable to an external clock from 75 to 750 kHz. Its current-mode architecture provides easy loop compensation, fast transient response, cycle-by-cycle overcurrent protection, and excellent line regulation. Output current sensing is accomplished by measuring the voltage drop across a sense resistor.
The LTC3863’s additional features include programmable soft start or tracking, overvoltage protection, short-circuit protection, and failure mode and effects analysis (FMEA) verification for adjacent pin opens and shorts.

HOBOlink can configure exported data export in a customized manner. For example, a user with four HOBO U30 systems measuring multiple parameters may configure HOBOlink to automatically export temperature data only. The time range may also be specified.

HOBOlink also enables users to easily access current and historical data, set alarm notifications and relay activations, and manage and control HOBO U30 systems without going into the field. An application programming interface (API) is available to organizations that want to integrate energy and environmental data from HOBOlink web servers with custom software applications.
Contact Onset for pricing.

Peregrine Semiconductor expanded its DuNE digitally tunable capacitor (DTC) product line with six second-generation devices for antenna tuning in 4G long-term evolution (LTE) smartphones. The PE623060, PE623070, PE623080, and PE623090 (PE6230x0) DTCs have a 0.6-to-7.7-pF capacitance range and support main antenna power handling of up to 34 dBm. The PE621010 and the PE621020 (PE6210x0) DTCs have a 1.38-to-14-pF capacitance range and are optimized for power handling up to 26 dBm, making them well suited for diversity antennas. The highly versatile devices support a variety of tuning circuit topologies, particularly impedance-matching and aperture-tuning applications.
The PE6230x0 DTCs are optimized for key cellular frequency bands from 700 to 2,700 MHz, featuring direct battery voltage operation with consistent performance enabled by on-chip voltage regulation.

The 5-bit, 32-state PE623060/70/80 DTCs have a 0.9-to-4.6-pF capacitance range. The 4-bit, 16-state PE623090 DTC has a 0.6-to-2.35-pF capacitance range. The PE623090 DTC’s lower minimum capacitance solves a critical problem in high-frequency tuning. The 5-bit, 32-state PE6210x0 DTCs support the 100-to-3,000-MHz frequency range. These DTCs extend the range of diversity antennas and improve data rates by optimizing the antenna performance at the operating frequency. The PE621010 DTC has a 1.38-to-5.90-pF capacitance range.

The May issue of Circuit Cellar provides a number of articles focusing on how to utilize measurements and sensors in your designs.

Knowing how to generate a magnetic field to calibrate a sensor can help with a number of

Winding 25 turns of 26 AWG enamel wire on a toroid is normally difficult, but that slit made it very easy. You would wind much smaller wire on a toroid used as an inductor.

DIY projects. Most electronic devices use inductors or transformers that depend on magnetic fields. In the May issue, Ed Nisley describes how he used a small ferrite toroid to produce a known magnetic field, which he utilized to calibrate some cheap Hall-effect sensors he obtained on eBay (p. 52).

“While the results certainly don’t transform cheap sensors into laboratory instruments, you can use them for tech jewelry with a clear conscience,” Nisley says. “You’ll also have a better understanding of magnetic fields, which may come in handy when you’re building inductors.”

Whether you’re designing a small controller for your own use or an electronic device for mass production, it’s important to keep “testability” in mind. So, it’s a good idea to make a dedicated tester for your product part of the design process at the outset. Such a tester can ensure your device is working properly in your workshop—before it ships to a customer. On page 56, George Novacek describes how an inexpensive tester can bolster an electronic device’s reliability and increase its marketability.

Brothers Robert and Donald Kunzig, both with backgrounds in the telecommunications industry, stepped outside the technologies most familiar to them when they took on an ambitious project—to produce an accurate and easy to use wireless, energy-usage monitor. They also wanted the monitor to hold its collected data even during a power outage or a router issue. Did they succeed? Check out their article on page 18 to find out.

The DNA sequencer’s design includes a motor controller, a light sensor amplifier, and an injector driver circuit.

While DNA, the molecule that provides genetic instruction to all living organisms, is complex, building a DNA sequencer can be relatively simple. Fergus Dixon used a light sensor amplifier, a motor controller, and an injector driver circuit to fulfill a customer’s request for a DNA sequencer with a color screen and full connectivity via Ethernet or Bluetooth (p. 26)

If you’re a DIYer who is nervous about possible levels of radiation in your home, find out how to build a hand-held radiation sensor on page 60.

Also, Jesús Calviño-Fraga describes how he built a serial port-to-SPI bridge programmer, the “S2S Dongle,” which functions without a pre-programmed microntroller (p. 34).

Finally, this issue includes articles that wrap up intriguing projects Circuit Cellar introduced in April.

Last month, Jeff Bachiochi explored the musical instrument digital interface (MIDI). In Part

An Atmel ATmega88 microcontroller is at the heart of the CNC router controller.

2, he focuses on a hardware circuit that can monitor the MIDI messages sent between his project’s MIDI devices, which include a Harmonix drum kit used with the Xbox version of the Rock Band video game (p. 68).

Brian Millier calls his construction of a microcontroller-based, G-code controller for a CNC router one of his most challenging DIY projects. The second article in his series focuses on two functional blocks: the axis controller and the host controller (p. 42.)

Whether you’re planning a small controller for your own use or an electronic device for mass production, you need to keep “testability” in mind. So, it’s a good idea to make a dedicated tester for your product part of its initial design.

Such a tester can ensure your device is functioning smoothly in your workshop—before it ships to a customer.

A dedicated tester (with the white panel) simulates inputs and loads for an embedded controller. A breakout box (with the red terminals on the panel) allows access to every interface line.

In the upcoming May issue of Circuit Cellar, columnist and engineer George Novacek discusses how to build a simple and inexpensive dedicated tester for a product.

“According to old engineering wisdom, every new project should begin with test design,” Novacek says in his column. “If you don’t follow this advice, your product may have features that are too awkward, too time-consuming, or impossible to test. You always need to keep testability in mind. Ultimately, it improves reliability, reduces manufacturing cost, minimizes field returns, speeds up production, and reduces the cost of repairs.”

Engineers certainly have access to a broad range of general testing equipment, from oscilloscopes to signal generators and analyzers.

“While these instruments are sufficient for testing, working with them solely may be slow and cumbersome,” Novacek says. “Imagine an embedded controller with a number of input and output devices, all of which need to be monitored while different signals are injected for the test. That’s where the dedicated tester comes in. Companies with deep pockets can purchase various types of automatic test equipment (ATE), but this may be too expensive for a small operation. Or, it may not be practical because of the complex setup for a low-volume production. Building a dedicated, inexpensive tester can solve the problem by ensuring an efficient and repeatable test.”

Check out the May issue of Circuit Cellar for more of Novacek’s guidance on why and how you should build a dedicated tester.

Novacek plans to continue examining product testability in upcoming issues, addressing topics that include the design of hardware and software that enables a product to be efficiently tested.

Tom Cantrell wanted to stop fiddling with his sprinklers as he tried to balance conserving water in California and keeping his lawn green. So he asked himself if he could craft a weather-savvy sprinkler controller.

In the April issue of Circuit Cellar, he describes how to weatherize an embedded app. He uses a Texas Instruments MSP430 microcontroller and a WIZnet W5200 smart Ethernet chip to access National Weather Service forecasts and data (p. 36).

Engineer and entrepreneur Michael Hamilton also has found that necessity breeds invention—which in turn can start a new business. “While working for Ashland Chemical in clean room environments, I realized there was a need for an accurate humidity controller,” he says. “This led me to design my own temperature and humidity controller and form my first company, A&D Technologies.”

In our interview, he talks about what he has done since, including founding another company and becoming an award-winning designer in the RL78 Green Energy Challenge (p. 44).

A shift in the timing signal—or jitter—of a digital transmission can adversely affect your high-speed designs. It’s been an issue for at least 40 years, with the advent of the first all-digital telecommunications networks such as PDH. But you may not have dealt with it in your designs. In the April magazine, Robert Lacoste explains how to diagnose a case of the jitters (p. 54).

Jeff Bachiochi isn’t a musician. But he didn’t need to be one to work with the musical instrument digital interface (MIDI), which relays instructions on how to play a piece directly to an instrument (bypassing the musician). In the April issue, he describes the circuitry needed to connect to MIDI communication and display messages between devices (p. 60).

Atmel’s ATmega88 and ATmega1284 microcontrollers are at the heart of the CNC controller.

Also, Brian Millier describes how he built a microcontroller-based G-code controller for a CNC router. Even if you are not interested in building such a controller, you can learn from the techniques he used to provide the multi-axis stepper-motor motion (p. 30).

You also might find Scott Weber’s experience instructive. After placing microcontroller-based devices throughout his home, he found he needed a control panel to enable him to update the devices and check on their operation. He shares his panel’s basic structure and its software design. Its display shows him all the information he needs (p. 22).

While wear and tear affect the reliability of hardware, software reliability is different. Whatever causes software to fail is built-in, through errors ranging from poor coding to typos to omissions. On page 51, George Novacek shares some methods of calculating the probability of faults in your firmware.

Also in the April issue, Bob Japenga continues looking at concurrency in embedded systems. In the sixth article of his series, he discusses two Linux mechanisms for creating embedded systems—POSIX FIFOs and message queues (p. 48).

Finally, “From the Archives” features a 2003 article by Mark Balch about Verilog HDL. He discusses how to use it in your custom logic designs for digital systems (p. 68).

In the open-source hardware development and distribution model, designs are created collaboratively and published openly. This enables anyone to study, modify, improve, and produce the design—for one’s own use or for sale. Open-source hardware gives users full control over the products they use while unleashing innovation—compared to the limits of proprietary research and development.

This practice is transforming passive consumers of “black box” technologies into a new breed of user-producers. For consumers, open-source hardware translates into better products at a lower cost, while providing more relevant, directly applicable solutions compared to a one-size-fits-all approach. For producers, it means lower barriers to entry and a consequent democratization of production. The bottom line is a more efficient economy—one that bypasses the artificial scarcity created by exclusive rights—and instead focuses on better and faster development of appropriate technologies.

Open-source hardware is less than a decade old. It started as an informal practice in the early 2000s with fragmented cells of developers sharing instructions for producing physical objects in the spirit of open-source software. It has now become a movement with a recognized definition, specific licenses, an annual conference, and several organizations to support open practices. The expansion of open-source hardware is also visible in a proliferation of open-source plans for making just about anything, from 3-D printers, microcontrollers, and scientific equipment, to industrial machines, cars, tractors, and solar-power generators.

As the movement takes shape, the next major milestone is the development of standards for efficient development and quality documentation. The aim here is to deliver on the potential of open-source products to meet or exceed industry standards—at a much lower cost—while scaling the impact of collaborative development practices.

The Internet brought about the information revolution, but an accompanying revolution in open-source product development has yet to happen. The major blocks are the absence of uniform standards for design, documentation, and development process; accessible collaborative design platforms (CAD); and a unifying set of interface standards for module-based design—such that electronics, mechanical devices, controllers, power units, and many other types of modules could easily interface with one another.

Can unleashed collaboration catapult open-source hardware from its current multimillion dollar scale to the next trillion dollar economy?

One of the most promising scenarios for the future of open source hardware is a global supply chain made up of thousands of interlinked organizations in which collaboration and complementarity are the norm. In this scenario, producers at all levels—from hobbyists to commercial manufacturers—have access to transparent fabrication tools, and digital plans circulate freely, enabling them to build on each other quickly and efficiently.

The true game changers are the fabrication machines that transform designs into objects. While equipment such as laser cutters, CNC machine tools, and 3-D printers has been around for decades, the breakthrough comes from the drastically reduced cost and increased access to these tools. For example, online factories enable anyone to upload a design and receive the material object in the mail a few days later. A proliferation of open-source digital fabrication tools, hackerspaces, membership-based shops, fab labs, micro factories, and other collaborative production facilities are drastically increasing access and reducing the cost of production. It has become commonplace for a novice to gain ready access to state-of-art productive power.

On the design side, it’s now possible for 70 engineers to work in parallel with a collaborative CAD package to design the airplane wing for a Boeing 767 in 1 hour. This is a real-world proof of concept of taking development to warp speed—though achieved with proprietary tools and highly paid engineers. With a widely available, open-source collaborative CAD package and digital libraries of design for customization, it would be possible for even a novice to create advanced machines—and for a large group of novices to create advanced machines at warp speed. Complex devices, such as cars, can be modeled with an inviting set of Lego-like building blocks in a module-based CAD package. Thereafter, CNC equipment can be used to produce these designs from off-the-shelf parts and locally available materials. Efficient industrial production could soon be at anyone’s fingertips.

Sharing instructions for making things is not a novel idea. However, the formal establishment of an open-source approach to the development and production of critical technologies is a disruptive force. The potential lies in the emergence of many significant and scalable enterprises built on top of this model. If such entities collaborate openly, it becomes possible to unleash the efficiency of global development based on free information flows. This implies a shift from “business as usual” to an efficient economy in which environmental and social justice are part of the equation.

Catarina Mota is a New York City-based Portuguese maker and open-source advocate who cofounded the openMaterials (openMaterials.org) research project, which is focused on open-source and DIY experimentation with smart materials. She is both a PhD candidate at FCSHUNL and a visiting scholar at NYU, and she has taught workshops on topics such as hi-tech materials and simple circuitry. Catarina is a fellow of the National Science and Technology Foundation of Portugal, co-chair of the Open Hardware Summit, a TEDGlobal 2012 fellow, and member of NYC Resistor.

Marcin Jakubowski graduated from Princeton and earned a PhD Fusion Physics from the University of Wisconsin. In 2003 Marcin founded the Open Source Ecology (OpenSourceEcology.org) network of engineers, farmers, and supporters. The group is working on the Global Village Construction Set (GVCS), which is an open-source, DIY toolset of 50 different industrial machines intended for the construction of a modern civilization (http://vimeo.com/16106427).

The March issue of Circuit Cellar includes articles from a number of practical problem solvers, such as a homeowner who wanted to get a better grasp of his electrical usage and a professor who built a better-than-average music box.

Dean Boman, a retired spacecraft communications systems designer, decided to add oversight of his electric usage (in real time) to his home-monitoring system. After all, his system already addressed everything from security to fire detection to irrigation control. On page 34, he describes his energy monitoring system, which provides a webpage with circuit-by-circuit energy usage. This level of detail can make you a well-informed energy consumer.

Dean Bowman’s energy-monitoring system

Bruce Land, a senior lecturer in electronics and computer science at Cornell University, thought developing a microcontroller-based music device would be a useful class lesson. But more importantly, he knew his 3-year-old granddaughter would love an interactive music box. On page 28, he shares how he built a music device with an 8-bit microcontroller that enables changing the note sequence, timbre, tempo, and beat.

Computer engineer Chris Paiano has written many application notes for the Cypress programmable-system-on-chip (PSoC) chipset. He is even working on a PSoC solution for his broken dishwasher. But that’s far from his most impressive work. Read an interview with this problem-solver on page 41.

College students built a rotational inverted pendulum (RIP) to test nonlinear control theory. But you might want to make and tune one for fun. Nelson Epp did. On page 20, he describes how he built his RIP and utilized a TV remote control to meet the challenges of balance and swing. “It is a good project because the hardware used is fairly common, the firmware techniques and math behind them are relatively easy to understand, and you get a good feeling when, for the first time, the thing actually works,” he says.

Nelson Epp’s rotational inverted pendulum (RIP)

Chip biometrics are unique digital chip features—left by the manufacturing process—that distinguish one chip from another of the same type. Finding these chip “fingerprints” is important in developing trustworthy and secure electronics. On page 45, Patrick Schaumont discusses how to extract a fingerprint from a field programmable gate array (FPGA) and authenticate a chip’s identity.

Maurizio Di Paolo Emilio, a telecommunications engineer from Italy, designs data acquisition system software for physics experiments and industrial use. In the Tech the Future essay on page 80, he discusses the many alternatives for data acquisition software and the goal of developing credit-card-sized embedded data acquisition systems, using open-source software, to manage industrial systems.

Other article highlights include George Novacek’s look at ways to reduce product failures in the field (p. 52), Ed Nisley’s take on how to get true analog voltages from the Arduino’s PWM outputs (p. 56), and Jeff Bachiochi’s guidance on using a development kit to design a tool to help transmit Morse code (p. 68).

With this issue’s emphasis on robotics, you’ll want to check out our From the Archives article about a SOPHOCLES design for a solar-powered robot that can detect poisonous gas (p. 62).

The answers to the Circuit Cellar 270 Engineering Quotient are now available. The problems and answers are listed below.

Problem 1: Given a microprocessor that has hardware support for just one level of priority for interrupts, is it possible to implement multiple priorities in software? If so, what are the prerequisites that are required?

Answer 1: Yes, given a few basic capabilities, it is possible to implement multiple levels of interrupt priority in software. The basic requirements are that it must be possible to reenable interrupts from within an interrupt service routine (ISR) and that the different interrupt sources can be individually masked.

Question 2: What is the basic scheme for implementing software interrupt priorities?

Answer 2: In normal operation, all the interrupt sources are enabled, along with the processor’s global-interrupt mask.

When an interrupt occurs, the global interrupt mask is disabled and the “master” ISR is entered. This code must (quickly) determine which interrupt occurred, disable that interrupt and all lower-priority interrupts at their sources, then reenable the global-interrupt mask before jumping to the ISR for that interrupt. This can often be facilitated by precomputing a table of interrupt masks for each priority level.

Question 3: What are some of the problems associated with software interrupt priorities?

Answer 3: For one thing, the start-up latency of all the ISRs is increased by the time spent in the “master” ISR. This can be a problem in time-critical systems. This scheme enables interrupts to be nested, so the stack must be large enough to handle the worst-case nesting of ISRs, on top of the worst-case nesting of non-interrupt subroutine calls.

Finally, it is very tricky to do this in anything other than Assembly language. If you want to use a high-level language, you’ll need to be intimately familiar with the language’s run-time library and how it handles interrupts and reentrancy, in general.

Answer 4: Yes, on most such processors, you can execute a subroutine call to a “return from interrupt” instruction while still in the master ISR, which will then return to the master ISR, but with interrupts enabled.

Check to see whether the “return from interrupt” affects any other processor state (e.g., popping a status word from the stack) and prepare the stack accordingly.

Also, beware that another interrupt could occur immediately thereafter, and make sure the master ISR is reentrant beyond that point.

As with wireless connectivity, when it comes to your engineering skills, range matters. The more you know about a variety of applicable topics, the more you’ll profit in your professional and personal engineering-related endeavors. Thus, it makes sense to educate yourself on a continual basis on the widest range of topics you can. It can be a daunting task. But no worries. We’re here to help. In this issue, we feature articles on topics as seemingly diverse as wireless technology to embedded programming to open-source development. Let’s take a closer look.

Consider starting with Catarina Mota and Marcin Jakubowski’s Tech the Future essay, “Open-Source Hardware for the Efficient Economy” (p. 80). They are thoughtful visionaries at the forefront of a global open-source hardware project. You’ll find their work exciting and inspirational.

Stuart Ball’s Dip Meter

On page 20, Stuart Ball describes the process of designing a digital dip meter. It’s a go-to tool for checking a device’s resonant frequency, or you can use it as a signal source to tune receivers. Ball used a microcontroller to digitize the dip meter’s display.

Interested in 3-D technology? William Meyers and Guo Jie Chin’s 3-D Paint project (p. 26) is a complete hardware and software package that uses free space as a canvas and enables you to draw in 3-D by measuring ultrasonic delays. They used a PC and MATLAB to capture movements and return them in real time.

This month we’re running the third article in Richard Lord’s series, “Digital Camera Controller” (p. 32). He covers the process of building a generic front-panel controller for the Photo-Pal flash-trigger camera controller project.

Richard Lord’s front panel CPU

Turn to page 37 for the fifth article in Bob Japenga’s series on concurrency in embedded systems. He covers the portable operating system interface (POSIX), mutex, semaphores, and more.

Check out the interview on page 41 for insight into the interests and work of electrical engineer and graduate student Colin O’Flynn. He describes some of his previous work, as well as his Binary Explorer Board, which he designed in 2012.

Colin O’Flynn’s Binary Explorer Board

In Circuit Cellar 270, George Novacek tackled the topic of failure mode and criticality analysis (FMECA). This month he focuses on fault-tree analysis (p. 46).

Arduino is clearly one of the hottest design platforms around. But how can you use it in a professional-level design? Check out Ed Nisley’s “Arduino Survival Guide” (p. 49).

Standing waves are notoriously difficult to understand. Fortunately, Robert Lacoste prepared an article on the topic that covers an experimental platform and measurements (p. 54).

This month’s article from the archives relates directly to the issue’s wireless technology theme. On page 60 is Roy Franz’s 2003 article about his WiFi SniFi design, which can locate wireless networks and then display “captured” packet information.

If you like this issue’s cover, you’ll have to check out Jeff Bachiochi’s article on QR coding (p. 68). He provides an excellent analysis of the technology from a pro engineer’s point of view.

We achieved three main goals by putting together this issue. One, we properly documented the history of Circuit Cellar from its launch in 1988 as a bi-monthly magazine
about microcomputer applications to the present day. Two, we gathered immediately applicable tips and tricks from professional engineers about designing, programming, and completing electronics projects. Three, we recorded the thoughts of innovative engineers, academics, and industry leaders on the future of embedded technologies ranging from
rapid prototyping platforms to 8-bit chips to FPGAs.

The issue’s content is gathered in three main sections. Each section comprises essays, project information, and interviews. In the Past section, we feature essays on the early days of Circuit Cellar, the thoughts of long-time readers about their first MCU-based projects, and more. For instance, Circuit Cellar‘s founder Steve Ciarcia writes about his early projects and the magazine’s launch in 1988. Long-time editor/contributor Dave Tweed documents some of his favorite projects from the past 25 years.

The Present section features advice from working hardware and software engineers. Examples include a review of embedded security risks and design tips for ensuring system reliability. We also include short interviews with professionals about their preferred microcontrollers, current projects, and engineering-related interests.

The Future section features essays by innovators such as Adafruit Industries founder Limor Fried, ARM engineer Simon Ford, and University of Utah professor John Regehr on topics such as the future of DIY engineering, rapid prototyping, and small-RAM devices. The section also features two different sets of interviews. In one, corporate leaders such as Microchip Technology CEO Steve Sanghi and IAR Systems CEO Stefan Skarin speculate on the future of embedded technology. In the other, engineers such as Stephen Edwards (Columbia University) offer their thoughts about the technologies that will shape our future.

As you read the issue, ask yourself the same questions we asked our contributors: What’s your take on the history of embedded technology? What can you design and program today? What do you think about the future of embedded technology? Let us know.